In thermal transfer printing successive sections of a donor sheet or web are fed through a linear printing region where they move, in contact with successive lines of a receiver, past a thermal print head comprising a linear array of selectively energizable, pixel size heater elements. The print head or other means urge the juxtaposed donor and receiver sections into intimate contact at the print zone so that dye is transferred from the donor to the receiver in the pixels beneath energized heaters of the array. In multicolor thermal printing the receiver is moved through the printing zone a plurality of times so that a plurality of different color image components (e.g. cyan, magenta and yellow) can be successively printed on the donor, in register.
One common configuration for effecting such multicolor printing is described in U.S. Pat. No. 4,745,413, wherein the donor sheet is clamped onto the periphery of a print drum which rotates successive line portions past a linear thermal print array. A web bearing successive donor sections of yellow, magenta and cyan dye is fed through the print zone, between the print array and receiver, in a timed relation so that a different color donor section moves through the print zone with the receiver, respectively during each of the print drum rotations.
Although not essential in thermal transfer printing, it is often desirable to heat and compress the dye image(s) on the surface of a receiver sheet. This post treatment, referred to as fusing, seals and stabilizes the dyes of the images and thereby enhances the keeping quality of the print. Such fusing has been accomplished by feeding the printed sheet through the nip of a fusing device comprising a heated roller and a pressure roller. The fusing device can be separate from the printer or located within the printer housing and positioned to receive the receiver as it is fed off of the printing drum.
Proper fusing of the dye image on receiver sheets depends upon the proper amounts of heat and pressure being applied uniformly to all areas of the image. To achieve these goals, prior art fusing devices have been fairly complex, e.g. requiring a heating drum with an accurately cylindrical periphery and expensive bearings and a pressure roller that is constructed and located with fairly high tolerances.